1. Field of the Invention
The present invention relates to semiconductor devices including a test circuit, and more particularly relates to a test circuit to change a semiconductor device to a test mode.
2. Background Art
It is an effective technique for manufacturing of semiconductor devices to improve efficiency of a shipping test to keep the quality of the devices and reduce its manufacturing cost. As a method to improve the efficiency of the test, some ICs are equipped with a test-mode function that is used only for the test, aside from functions that are used by users. Such a test mode is equipped with unique functions other than functions that users require, such as a function to output an internal node state and a function to rewrite a memory IC by one operation, and so can improve the efficiency of the test. Such test-mode functions require a method to implement the mode in a state that is not available by users, and a configuration for changing has to be devised so as not to let a user change the device into the test mode erroneously. An available method to change the semiconductor device into a test mode includes implementing a test mode function using a test terminal (see Patent document 1, for example).
[Patent Document 1] Japanese Patent Application Laid-Open No. 2007-67180